Electric fuse



E. V. SUNDT ELECTRIC FUSE Feb 5, i957 Filed May 18, 1953 United States Patent G This invention relates to electric fuses for protecting electric circuits from overload conditions.

The principal object of this invention is to provide an improved fuse which embodies a new principle of construction and operation, which provides new and improved results, which prevents the establishment of a sustained arc, which prevents the building up of excessive pressures in the fuse, which protects against high overloads even of small duration, which may protect against low overloads over periods of time, which quickly visually indicates the conditions of the fuse, and which may be inexpensively manufactured.

Briefly, the electric fuse of this invention includes a thin sheet conductor of fuse metal, and a rod shaped conductor having its end engaging and preferably secured to one side of the thin sheet conductor at a point within the area of the thin sheet conductor. Preferably, the transverse dimensions of the point of engagement of the conductors is greater than the thickness of the thin sheet conductor and the cross sectional conductive area of the thin sheet conductor immediately about the point of engagement is less than any other cross sectional conductive area of the thin sheet conductor. The conductors are connected in series with the electric circuit to be protected so that, upon a predetermined overload in the elec tric circuit, fusion takes place in the area of the thin sheet conductor about the point of engagement of the conductors and provides an ever widening gap between the conductors. This results in the arc, after striking, being unable to establish itself in one place long enough to cause damage. The establishment of sustained arcs is therefore prevented and the arc is quickly extinguished. Building up of excessive or dangerous pressures in the fuse upon the blowing of the fuse, is also prevented by reason of the quick extinguishment of the arc.

The thin sheet conductor of the fuse may be provided with indicia, such as for example 0. K., for indicating the condition of the fuse, these indicia being located on the opposite side of the thin sheet conductor adjacent the point of engagement of the conductors. When the thin sheet conductor fuses, upon blowing of the fuse, the indicia are at the same time obliterated. The indicia are readily visible through a transparent window in the fuse for checking the condition of the fuse.

In the operation of the electric fuse of this invention, the fuse blows on high overloads because the high current density, in the area of the thin sheet conductor around the point of engagement of the conductors, heats up the thin sheet conductor to its fusion temperature for instantly melting the same on high overloads, as for example, above 500% of the fuse rating, which would be caused by shorting or the like. The fuse also blows under another condition, a sustained low overload condition. Here, the point engagement of the conductors heats up to the fusion temperature of the thin sheet conductor by reason of current passage, and is so designed to be a factor in sustained overloads which may be only 125% of the fuse rating.

In order to prolong the time interval required to blow the fuse on low overload conditions, the rod shaped con- 'ice duetor may be made tubular at its end adjacent the point where it engages the thin sheet conductor and filled with a fuse metal which is of lower melting point than that of the thin sheet conductor. The fuse metal, preferably a eutectic alloy, absorbs considerable heat before it changes from solid to liquid at the fusion temperature thereof. This fuse metal, in intimate contact with the rod shaped conductor, causes the temperature of the rod shaped conductor to follow substantially that of the fuse metal. As a result, additional lag or time delay is obtained in raising the temperature of the point of engagement of the conductors to the value necessary to fuse the thin sheet conductor. This is true for two reasons: one, heat, and therefore watts, are required to bring the temperature of the rod shaped conductor up to melting point of its fuse metal because of its specific heat, and two, on reaching this temperature no further rise in temperature takes place until this fuse metal is melted because of the latent heat of fusion thereof. In this way, long time delays may be obtained which are useful in circuits having motors, solenoids, magnets and other equipment having high starting currents.

The electric fuse of this invention may be embodied in any desired type of fuse, such as for example, a plug type fuse or a cartridge type fuse. In the case of the former, the conductors of the fuse are electrically connected to the usual metal screw shell and the metal contact rivet and the indicia is located adjacent the transparent window in the end of the plug body. ln the case of the latter, the conductors are electrically connected to the usual metal fuse caps. The condition of the fuse may be seen through the tubular wall of the fuse body which may be made of transparent material.

v Further objects of this invention reside in the details of construction of the electric fuse and in the cooperative relationships between the component parts thereof.

Other objects and advantages of this invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawings in which:

Figure 1 is a perspective view of one form of the electric fuse of this invention.

Figure 2 is a top plan View of the electric fuse illustrated in Figure l but showing the condition of the fuse after the same has blown.

Figure 3 is a vertical sectional view taken substantially along the line 3 3 of Figure 2 but illustrating the fuse in operative condition.

Figure 4 is a view similar to Figure 3 but showing another form of the electric fuse of this invention.

Figure 5 is a vertical sectional view through still another form of the electric fuse of this invention.

Figure 6 is a sectiona vrew taken substantially along the line 6-6 of Figure 4.

Referring iirst to Figures l to 3 one form of the electric fuse of this invention is generally designated at 10, it being a plug type electric fuse. The electric fuse includes a hollow plug member 11 made of suitable insulating material such as Bakelite or ceramic and which is provided with an end wall. A metal screw shell 12 is suitably secured to the exterior of the plug member 11 and forms one of the electrical connectors for the fuse. A metal contact rivet 13 is secured to and extends through the end wall of the plug member 11 and forms the other electrical connection of the fuse. A thin sheet conductor 14 formed of suitable fuse material and having a substantial planar dirnension and a thickness suicient to be self-supporting is located within the fuse member and has an extension 15 which extends through an opening 16 in the plug member and is secured as by soldering or welding to the metal screw shell 12 as indicated at 17.

Vof the thin sheet conductor 14 at a point 2() within the planar area of the thin sheet conductor. Preferably the rod shaped Vconductor 18 is secured to the thin sheet conductor 14 by Welding or the like to assure goodelectrical contact, the welding being accomplished by condenser welding. Thus, an electric circuit is established through the electric fuse from the metal screw shell 12 through the thin sheet conductor 14 and the rod shaped conductor ,18 to the 'metal contact rivet 13 and in this way the electric fuse may be incorporated in an electric circuit for prote'cting the same. f ;l

The.transversedirnensions of vthe rod shaped conductor 18 and, hence, the point .of engagement V2t) of the conductorslS and. 14 are greater thanthe thickness of the thin sheet conductor 14. For example, the transverse dimension 'or Ydiameter of the rod shaped conductor V18 and, hence, the `'point of engagement 20 of the conductors may range from .O to .O60 inch while the thickness 'of the thinsheet conductor 1d may range from 003 to .010 inch, thesejdimensions depending on the fuserrating. The cross sectional conductive area of the thin sheet conductor immediately about the engaging or securing point 20 is less than any other cross sectional conductive area of the thin sheetconductor, These` dimensions are particularly applicable in connection with fuses of l3() amperes or less where the thin sheet conductor 14 is made of an alloy such as 98.5% zinc and 1.5% copper. A s -The 'open end of the plug member 11 may be closed by a'transparent window 21 which may be heldin place on the plug member by means of a suitable ring 22. The upper side ofthe thin sheet conductors 14 adjacent the point of engagement 20 may be provided with suitable indicia such as 0. K. as indicated at 23 in Figure l and this indicia is readily visible through the transparent windowzl.

The electric'fuse 10 is adapted to protect electric circuits againsty two types of overloadsY in the circuit, namely, a high overload such as caused by shorting of the circuit and a low overload persisting over a predetermined intervalof time. Y n

When a high overload occurs in the circuit, as for example, an overload of 500% of the rating of the fuse, a heavy current ow instantly-passes through the fuserand as a result there is a high current density in the thin sheet conductor 1,4 immediately adjacent the point of engagement 20. .This high current density instantly Amelts the thin sheet conductor at this point for the purpose of breaking the circuit. When fusion at this point takes place, an ever widening gap between the point of engagement 20 and the remainder of the thin sheet conductor 14 is broughtwabout. This in turn results in the arc, after striking,-'being unable to establish itself in one Aplace long enough to cause damage.V ln otherwords, it is as if the arc. had arlinnite number of places at vwhich it can strike in the area surrounding'the point of engagementf2tl. The result ,is that the arc is quickly extinguished and the establishment. of sustained arcs is effectively prevented. When lthe thin sheet conductor .14- is so fused, as indicated at 24 in-Fignre 2, lthe indicia 23 is at the same time Yobliteratedso that when thefuse is blown by an overload condition, this is readilydiscernible through the transparent window 21. .lIf a low overload condition persists in the circuit Ybeing protected for a relativelylong period of time, as for example, an overload of 125% of the rating of the fuse, the increased current ilowA heats the rod shaped conductor 13 and the. point of engagement 2G. vFollowing an interval of time, 'required to heat the point of engagement 20 up to the ffusion temperature of the thin sheet vconductor 14, the thin sheet conductor 14 then rapidly melts at this point for the purpose of breaking the circuit. Here also,

an ever widening gap between the point of engagement 20 and the remainder of the thin sheet conductor takes place with the resultant beneficial results described above. Delayed melting of the thin sheet conductor 14 on low overload conditions is aiorded by the time required to raise the temperature of the rod shaped conductor 18 and, hence, the point of engagement Ztrup to the fusion temperature of the thin, sheet conductor 14. Conversely, immediate melting of the thin sheet conductor 14 onV high overload conditions is brought about by reasonv of the fact that the thickness of the thin sheet conductor 14 is considerably less than 'the transverse dimensions of the rod shaped conductor 1S so that the current density in the thin sheet conductor 14 is considerably greater than that in the rod shaped conductor 1S. Y

Figure 4 illustrates another form of the invention wherein provision is made for increasing the elapsed time required for blowing the fuse on sustained low overload conditions. `With one exception the fuse or" FigureV 4 is like that shown in Figures l to 3 and it operates in the `same manner and accordingly like reference characters have been utilized forlike parts. ln Figure V4, the rod shaped conductor 1S has been hollowed out or madel tubular and is lied with a fuse metal 19 which is of lowerV melting point than that of the thin sheet conductor le. This fuse metal 19 may be a eutectic alloy, such as 63% tin and 37% lead, and absorbs considerable heat before it changes from solid to liquid at its fusion temperature. This fuse metal 19, which is in intimate contact with the rod shaped conductor 15, causes the temperature of the rod shaped conductor 18 to follow substantially the temperature of the fuse metal 19. ln this way the temperature of Athe rod shaped conductor 18 is held down to the liquefying temperature of the fuse metal 19 until it is fully melted. ln other words, increasedlag or time delay is here brought about because of two factors, one, heat, and therefore watts, are required to bring the temperature up tothe melting point o't the fuse metal because of its specic heat, and two, on reaching the temperature no further Vrise in temperature takes place until the fuse metal is melted due to the latent heat of fusion thereof. In this way long time delays may be obtained which are useful in circuits having motors, solenoids, magnets and other equipment having high starting currents and yet the electric circuit is protected against low overloads existing over long periods of time.

The electric fuse generally designated at Z6 in Figures 5` and 6 is 'a cartridge type fuse which is somewhat different in construction, but which operates in the saine manner as the plug type fuse 1G illustratedin Figures 'l to 4. In Figures 5 and 6 the cartridge type fuse 26 in- 'cludes a tube. member 27 formedof suitable insulating material such as ceramic, giass or the like and preferably Ait 'is made transparent so that the condition of the fuse 'maywlbe visually determined. r[he endso the tubular memberf27 are closed by conventional metalfus'ecaps 28 and 29. Albin sheet conductor Si) is Ylocated within vthe tubular member 27 and is provided with an extension 31 which is Velectrically connected to the fuse cap 29;. A rod shaped Yconductor 32 is located within the tubular member 27 and is carried and electrically connected by a member 33 secured to the other fuse cap 231 The end ofthe rod shaped conductor 32 engages one "slide 'of the thin sheet conductor 3! at a point within the. area of the thin Vsheet vconductor and pret biy the conductors are secured together as by condensatwelding or the like. The manner 'of ope-fatica 'of cartridge type fuse 26 is the same as that described above in connection with the plug type fuse 16 and, therefore, a further` description is not considered necessary. Here, the condition of the fuse is visually determined through the transparent tubular member -27 andthe thin sheet conductor 3% may be provided with indicia similar io the indiciaV 23 of the electric `fuse 1Q. Here, alsa, vthe rod Ashaped conductor '32 may or may not be providedwith annonce a low melting point fuse metal depending upon whether or not prolonged low overload protection is desired.

While for purposes of illustration several forms of this invention have been disclosed other forms thereof may become apparent to those skilled in the art upon reference to this disclosure and, therefore, this invention is to be limited only by the scope of the appended claims.

I claim as my invention:

l. An electric fuse comprising a thin sheet conductor of fuse metal, a rod shaped conductor h-aving fuse metal of lower melting point than that of the thin sheet conductor and having its end engaging one side of the thin sheet conductor at a point within the area of the thin sheet conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined high overload in the electric circuit which may be of short duration, or upon a predetermined low overload existing for an extended interval of time, fusion takes place promptly in the area of the thin sheet conductOr 4about the point to provide an ever widening gap vbetween the conductors.

2. An electric fuse comprising a thin sheet conductor of fuse metal, a rod shaped conductor having a fusible eutectic alloy of lower melting point than that of the thin sheet conductor and having its end engaging one side of the thin sheet conductor at a point within the area or" the thin sheet conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined high overload in the electric circuit which may be of short duration, or upon a predetermined low overload existing for an extended interval of time, fusion takes place promptly in the area of the thin sheet conductor about the point to provide an ever widening gap between the conductors.

3. An electric fuse comprising a thin sheet conductor of fuse metal, a rod shaped conductor having fuse metal of lower melting point than that of the thin sheet conductor and having its end engaging one side of the thin sheet conductor at a point within the area of the thin sheet conductor, the transverse dimensions of the point of engagement of the conductors being greater than the thickness of the thin sheet conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined high overload in the electric circuit which may be of short duration or upon a predetermined low overload existing for an extended interval of time, fusion takes place promptly in the area of the thin sheet conductor about the point to provide an ever widening gap between the conductors.

4. An electric fuse comprising a thin sheet conductor of fuse metal, -a rod shaped conductor having a fusible eutectic alloy of lower melting point than that of the thin sheet conductor and having its end engaging one side of the thin sheet conductor at a point within the area of the thin sheet conductor, the transverse dimensions of the point of engagement of the conductors being greater than the thickness of the thin sheet conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined high overload in the electric circuit which may be of short duration or upon a predetermined low overload existing for an extended interval of time, fusion takes place promptly in the area of the thin sheet conductor about the point to provide an ever widening gap between the conductors.

5. An electric plug fuse comprising a hollow plug member having an external metal screw shell and a metal contact rivet forming electrical connections for an electric circuit and a transparent window, a thin sheet conductor of fuse metal in the plug member adjacent the transparent window and electric-ally connected to the metal screw shell, a rod shaped conductor having fuse metal of lower melting point than that of the thinl sheet conductor in the plug member and electrically connected to the metal contact rivet and having its end engaging the under side of the. thin sheet conductor at -a point within the area of the thin sheet conductor, the arrange ment being such that, upon a predetermined high overload in the electric circuit or upon a predetermined low overload existing for an extended interval of time, fusion takes place in the area of the thin sheet conductor about the point to provide an ever widening gap between the conductors.

6. An electric cartridge fuse comprising a hollow tube member having a metal fuse cap at each end forming electrical connections for an electric circuit, a thin sheet conductor of fuse metal in the tube member electrically connected to one of the metal fuse caps, a rod shaped conductor having fuse metal of lower melting point than that of the thin sheet conductor in the tube member and electrically connected to the other metal fuse cap and having its end engaging one side of the thin sheet conductor at a point within the area of the thin sheet conductor, the arrangement being such that, upon a predetermined high overload in the electric circuit or upon a predetermined low overload existing for an extended interval ot time, fusion takes place in the area of the thin sheet conductor about the point to provide an ever widening gap between the conductors.

7. An electric fuse comprising a thin sheet conductor of fuse metal having a substantial planar dimension and a thickness sutlicient to be self-supporting, a rod-shaped conductor arranged normal to the thin sheet conductor and having its end physically and electrically conductively secured to one side of the thin sheet conductor at a point within the planar area thereof, the transverse dimensions of the securing point between the conductors being greater than the thickness of the thin sheet condoctor and the cross-sectional conductive area of the thin sheet conductor immediately about the securing point being less than any other cross-sectional conductive area of the thin sheet conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion .takes place in the area of the thin sheet conductor about the securing point to provide an ever-widening gap between the conductors.

8. An electric fuse comprising a thin sheet conductor of fuse metal having a substantial planar dimension and a thickness suicient to be self-supporting, a rod-shaped conductor arranged normal to the thin sheet conductor and having its end physically and electrically conductively secured to one side of the thin sheet conductor at a point within the planar area thereof, the transverse dimensions of the securing point between the conductors being greater than the thickness of the thin sheet condoctor and the cross-sectional conductive area of the thin sheet conductor immediately about the securing point being less than any other cross-sectional conductive area of the thin sheet conductor, a receptable having external electrical connections, and means for mounting the conductors in the receptacle and connecting the same in series with the electrical connections and hence in series in an electric circuit so that, upon a predeterminedoverload in the electric circuit, fusion takes place in the area of the thin sheet conductor about the securing point to provide an ever-widening gap between the conductors.

9. An electric fuse comprising a thin sheet conductor of fuse metal having a substantial planar dimension and a thickness sutlicient to be self-supporting, a rod-shaped conductor arranged normal to the thin sheet conductor and having its endvphysically and electrically conductively secured to one side of the thin sheet conductor at a point within the planar area thereof, the transverse dimensions of the securing point between the conductors being greater than the thickness of the thin sheet conductor and the cross-sectional conductive area of the thin sheet conductor immediately about the securing point being less than any other cross-sectional conductive area of the thin sheet conductor, indicia on the opposite side of the thin sheet conductor adjacent the securing point 'between the conductors' for indicating the condition of the electric' fuse, a receptacle having external; electrical connections and a transparent window, and means for mounting the conductors in thereceptacle with the indicia visible through the transparent window and with the yconductors inv series with the electrical lconnections and hence in series in an electric circuit so that, upon a predetermined overload in the 'electric circuit, fusion takes place in the area of the thin sheet conductor about the securing point, to provide an everwidening gap between the conductors, and for obliterating the indicia.

'10. An electric plug fuse comprising a hollow plug member having an external screw shell vand a metal contact rivet`forming electricalconnections for an electric circuit 'and a transparent window', a thin sheet conductor offusemetal in the plug member adjacent and parallel to the transparent window and Velectrically connected to vthefnietal screw shell 'and having a substantial planar dimension and athickness sufcient to be self-supporting, ajrod-shaped conductor in the plug member electrically connected to the 'metalcontact rivet `and arranged normal to the thin sheet conductor and having its end physically and electrically conductively secured to the under 's'ideiof thethin sheet conductorfatV a point within the planar area thereof, the' transverse dimensions of'the securing point between the conductors being greater than 1the .thickness of vthe thin sheet conductor and thecrosssectional conductive areaof the thin sheet conductor immediately about the Ysecuring ypointbeing less thanany other cross sectionalconductive area o f the thin sheet conductor, said conductors being connected `in 'series `through said screw shell' and contact rivet lso'that,*upon va pretermined voverload inthe electriccircuit, fusion takes place in the area of. the thin sheetconductor about the securing point, to provide an vever-widening gap between the conductors.v i

' 11. An electric plug fuse comprising av hollow Vplug member having an external' screw shell and a m etal contact rivet forming electrical connections for an electric vcircuit and a transparentV window, a thin sheet conductor lof fuse metal-in the plug member adjacent and parallel Vindicating the condition of the electric fuse, the transverse dimensions of the securing point between the conductors being Agreaterthan the 'thickness of the thin sheet conductor and the cross-:sectional conductive area of the vthin Vsheet conductor immediately about the securing point being less thanany other cross-sectional conductive area ofthe thin sheet conductor, saidy conductors being con- "nected'in series through said screw shell and contact r r ivet'so that',' upon a predetermined overload inthe electrie circuit, fusionV takes place in ythe area of the thin vsheet conductor about the securing point, to provide an ever-Widening gap between the conductors andfor oblitera'ti'ng the indicia.

i '12." An electriccartridge fuse comprising a hollow tube member having a metal fuse cap at each end forming electrical connections for an electric circuit, a thin sheet conductor of fuse .metal in the tube member electrically connected to oneof themetal fuse caps and having a substantial planar dimension and a thickness suflicient toV its end physically and electrically conductively secured to one side of theV thin sheet conductor at aV point within the planar area thereof, the transverse dimensions of Vthe securing'point betweenthe conductors being greater than thethickness of 'the thin sheet conductor and the cross sectionalconductive 'area of the thin sheet conductor immediately about the securing point being less'than any be Vself supporting, a rod-shaped conductor in the tube Y member electrically connected to the Aother fuse cap and arranged normalV to the thinshee't'conductor and having other cross-sectional conductive area of the thin sheet conductor, said conductors being connected in series through' said fuse caps s o that, upon apredetermined overload in the electric circuit, fusion takes place in the area o f the thin sheet conductor about the securing point to provide an ever-widening gap between the conductors.

13. An electric fuse comprising a thin sheet conductor of fuse 'rnetal'h'aving' a substantial planar dimension and a thickness sufficient to be self-supporting, ated-shaped conductor arrangedl normal to the thin sheet conductor and having fuse metal of lower melting point thanthat of the thin sheet conductor and having its end physically and electrically conductively secured to one side of the thin sheet conductor at a pointwithin the planar area thereof, the transverse dimensions of the securing point between theconductors being greater than the thickness of the thin sheet conductor and the cross-sectional conductive area of the thin sheet 'conductor immediately about the securing point being less than any other crosssectional conductive area'of the thin sheet conductor,`and means for connecting the conductors-in series in an electric circuit so that, upon a predetermined high overload in the electric circuit which Amay be of short duration, or upon a predetermined low overload existing for an extended interval Aof time, fusion takes place promptly in the area of the' thin' sheet conductor about the securing point to provide an ever-widening gap between'the co'nductors.

14. An electric fuse comprising a thin sheet conductor of fuse metal having a substantial planar dimension and a thickness suicient to be self-supporting, a rod-shaped conductor arranged normal to the thin sheet conductor and having a fusible eutectic alloy of lower melting point than that of the thin sheet conductor and having its end physically and electrically conductively secured to one side of thethin sheet conductor at a point within the planar area thereof, the transverse dimensions of the securing point between the conductors being greater than the thickness of the thin sheet conductor and the crosssectional conductive area of the thin sheet conductor irnmediately about the securing point being less than any other cross-sectional conductive area of the thin sheet conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined high overload in' the electric circuit which may be of short duration, or upon a predetermined low overload existing for an extended interval of time, fusion takes place promptly in the area of the thin sheet conductor about the securing point to provide an ever-widening gap between the conductors.

ReferencesCited in the le of this 'patent UNITED STATES PATENTS 601,492 Blackwell Mar. 29, 1898 1,200,700 Berry Oct. 10, 1916 1,422,122 Nelson July 11, 1922 1,508,402 Kubiak Sept. 16, 1924 1,677,298 Sandin July 17, '1928 1,841,686 Stephenson Ian. 19, 1932 1,878,204 Trumbull et al Sept. 20, 1932 'i 1,944,145 Ginderv Jan. 16, 1934 2,050,940 Y Falk Aug. l1, 1936 2,067,977 Muncheryan Jan. 19, 1937 2,106,109 Prendergast Jan. 18, 1938 2,218,274 Wood Oct. 15, 1940 FOREIGN PATENTS 

